Firstly disconnecting the battery wont and cant re-write the cars ECU back to stock thats a myth. The ME9 ECU stores its info on solid state chipsets not a temporary flash memory that requires a voltage to retain its memory.
Disconnecting a battery wont clear any fault codes either if anything its more likley to add a few! nothing will be reset as such by disconnecting a battery.
The fuel issue I have seen a few times, the car may be running in a limp mode, often caused by too much ignition advance for the conditions/fuel type, ECU sensing knock and pulling loads of timing. Get the fault codes read and cleared and then carry out a throttle body adaptation (Engine, basic settings, block 60) and this should solve your problem.
I am hoping that your car was remapped proffesionally and datalogged / dyno tested to create an accurate map rather than a '1 size fits all guestimap'